With funding from AHRQ, we studied preventable adverse drug events among 30,000 older adults treated in the ambulatory setting by a multispecialty group practice over a one year period. The overall rate of adverse drug events was 50.1 per 1000 person-years, with a rate of 13.8 preventable adverse drug events per 1000 person-years. Of the serious, life-threatening and fatal ADEs, 244 or 42% were judged to be preventable. During that study we also identified errors that were the proximal causes of these serious, life-threatening and fatal preventable events: drug interactions, medications conflicting with recent laboratory values indicating high risk, medications for which patients had a history of allergies or prior reactions, lack of accompanying prophylaxis for known side effects, excessive dosing, inadequate laboratory monitoring; failure to act on monitoring (e.g., high INR levels in patients on warfarin), and medications that were not appropriate for a patient's medical conditions. Working collaboratively with the Fallen Clinic of Central Massachusetts, the group practice that served as the base for our prior study, and with consultation from a senior risk assessment expert, we propose to examine the underlying processes leading to these serious errors, identify potential intervention points, and prepare action plans for implementation. [unreadable] [unreadable] Our aims are to: 1. Use probabilistic risk assessment to: a. characterize systemic and behavioral elements that increase the risk of serious errors in prescribing and monitoring medications for older adults in the ambulatory care setting and b. identify potentially high-yield and likely-to-be-successful interventions for lowering rates of preventable adverse drug events in that setting. 2. Estimate likelihood that interventions at any given step would be successful in reducing errors at that step and select interventions for implementation. 3. Develop action plans for implementing identified interventions. [unreadable] [unreadable] [unreadable]